This invention relates to marine seismic prospecting and, more particularly, to a connection system for attaching equipment to and detaching equipment from marine seismic cables.
A marine seismic streamer is a cable, typically several thousand meters long, that contains arrays of hydrophones and associated electronic equipment along its length. One purpose of the streamer is to position the hydrophone array at a known depth and orientation relative to a towing vessel in a survey area. Externally mounted equipment, such as depth controllers, called “birds,” streamer recovery pods, and acoustic pods, performs the functions of positioning and controlling the cable. Individual devices of these kinds of external equipment are attached to the streamer at various positions along its length. All of these external devices should be both attached to and removed from the cable as quickly and reliably as possible. Operational expenses of seismic vessels require rapid attachment and detachment of these external devices. Because these external devices typically cost thousands of dollars, they demand the highest degree of reliability from any attachment scheme. Cable attachment failures caused by connector failures or by cable accidents result in a significant financial loss both in time and in expensive equipment.
Today's typical cable attachment solutions consist of a collar arrangement that relies on a hinge and latch mechanism for operation. Examples of these mechanisms are described in U.S. Pat. No. 5,507,243, “Connector For Underwater Cables,” Apr. 16, 1996, to Oneil J. Williams et al. and in U.S. Pat. No. 5,709,497, “Latching Device,” Jan. 20, 1998, to David W. Zoch et al. External devices attached to the collars are clamped around races on the cable as the cable is payed out from the back deck of a survey vessel. The races allow the cable to rotate inside the collars while the external devices do not rotate as they are towed along. Conventional connector schemes usually require one operator to position and hold the awkward external device in place while a second operator secures the manual latching collars to the cable, often while trying to maintain balance on a rolling survey vessel. Requiring two operators significantly increases the cost of operation.
These conventional mechanisms also incorporate springs or pins having dissimilar metals in contact with the collar. Dissimilar metals in contact in seawater corrode because of galvanic reactions. While conventional hinge-and-latch collars offer quick attachment and removal when new, exposure to salt water degrades their performance and can eventually lead to their complete failure. A failed collar can result in the loss of an external electronic device or a jammed connector on the seismic cable, which costs time in removing external devices as the cable is reeled in.
A thick cross section (typically of aluminum) is required to safely imbed a conventional latching mechanism within the collar. Such a large cross section creates hydrodynamic noise and lateral accelerations on the seismic cable as it is towed through the water. These undesirable characteristics corrupt the sensitive measurement of seismic acoustic signals by the hydrophones.
The Quick Cuff™ connector, sold by ION Geophysical Corporation of Houston, Tex., U.S.A. and described in U.S. Pat. Nos. 6,263,823 and 6,397,773, “Connector System for Connecting Equipment to Underwater Cables,” Jul. 24, 2001, and Jun. 4, 2002, to André W. Olivier, avoids many of those shortcomings and provides these advantages: a marine cable connection having no moving parts, which is more reliable than prior art connections; a marine cable connection that performs the same whether brand new or aged as a result of long term exposure to seawater; a marine cable connection that requires fewer operators to safely operate; a marine cable connection with a lower hydrodynamic noise profile because of the lack of a salient attachment mechanism; a marine cable connection that can readily be adapted to both existing seismic cables as well as new technology cables; a marine cable connection that is lighter and simpler than existing connectors; a marine cable connection that consists of an inner race and an outer collar engaged by means of geometrical features rather than a mechanism; and a marine cable connection that is significantly quicker to operate than prior art connectors. The Quick Cuff™ connector system includes a cuff attached to a device, such as a cable-leveling or -steering bird or an acoustic transceiver, to be connected to the streamer cable at a known location. The C-shaped cylindrical cuff has a circular inner surface interrupted by a gap. A throat is formed by the gap in the cuff extending the length of the cuff. The spacing between the ends of the C across the throat defines the width of the gap. The width of the gap is slightly larger than the diameter of the streamer cable so that the cuff can slip onto the cable. An inner collar having a race is affixed to the cable at a known location. The diameter of the race is greater than the width of the gap formed by the cuff's throat. The inner surface of the cuff can be slid into position on the race of the inner collar. Because the diameter of the race exceeds the width of the gap of the throat, the cuff and the attached equipment cannot disconnect radially from the inner collar. Structural elements, such as retainer pins extending from the external device through a slot in the cuff and into a groove on the collar, further hinder longitudinal displacement of the cuff along the inner collar. But some devices, such as streamer recovery pods not sold by ION Geophysical Corporation, do not have retainer pins, and, in some marine conditions, such as a following sea, these external devices may be pushed forward so that the cuffs disengage the races.